The present invention relates to anesthesia systems used to provide an anesthetic agent to a patient.
In general, anesthesia systems are utilized in medical settings and comprise various equipment to anesthetize the patient and maintain the patient in an anesthetized state until an operation or procedure is completed. Such systems typically comprise various pressure regulators, flow control devices, gas mixing devices and vaporizers to vaporize a volatile liquid anesthetic and to introduce the anesthetic laden gases into the patient. The patient is connected to the system by means of a face mask or other device and which interfaces with the anesthesia system via a patient circuit that may typically have an inspiratory limb through which the gases are introduced into the patient and an expiratory limb that conveys the exhaled gases from the patient. Such limbs may be separate conduits joined by a wye piece at or near the patient or may comprise co-axial conduits commonly known as Bain circuits.
In a typical anesthesia system, the overall flow of gases to and from the patient may be in a generally closed circuit, that is, the patient is connected to a substantially closed loop supply of gases and re-breathes certain of those exhaled gases supplemented by fresh gas. Alternatively, the patient circuit could be an open circuit and all of the exhaled gases simply vented or channeled from the system to an external environment and not re-breathed by the patient. Other variety of circuits are used that deliver the anesthetic gases to the patient, such as semi-open circuits and the like.
As the driving force to the patient, a ventilator is used and which basically breathes for the patient since the patient is under anesthesia and is unable to carry out the normal spontaneous breathing functions. The ventilator, therefore, provides a quantity of gas containing a predetermined metered quantity of the anesthetic agent along with other gases such as nitrous oxide (N2O) and, of course, a life sustaining percentage of oxygen.
Anesthesia systems that employ a closed circuit supply of gases typically include a canister that contains absorbent material to remove carbon dioxide (CO2) from the patient gas. Periodically, the absorbent material becomes extinguished and the canister needs replacing. If the canister is replaced while the anesthesia machine is in use, two things can occur: patient circuit gas is released into the room while the canister is off, or there is no loss of patient circuit gas if the breathing system is equipped with a CO2 bypass mechanism. The latter arrangement is addressed by the present invention.
When the CO2 bypass mechanism is actuated by the removal of the absorbent canister, the breathing circuit functions as normal, except for the removal of CO2. This is acceptable for a short period of time until a new canister is substituted. It is during CO2 bypass that awareness should be maintained that the machine is operating in the bypass mode. However, distractions can occur that remove the caregiver's attention from installing a new canister. Once attention is regained, the user may fail to notice the missing canister because the system appears to be functioning normally. If the system continues to operate without the CO2 bypass, serious medical complications to the patient can occur.